Currently, in order to form an interlayer insulating layer and the like of an organic light-emitting device, photosensitive polyimide that has heat resistance is actively used.
The photosensitive polyimide is advantageous in that physical properties such as heat resistance, mechanical strength and the like are excellent, there are excellent electric properties such as low dielectricity, high insulating property and the like, planarization property on a coated surface is good, the content of impurity that reduces the reliability of a device is very low, and fine shapes are easily obtained.
Polyimide may be classified into a negative photosensitive polyimide and a positive photosensitive polyimide, but many studies have been actively made of the positive photosensitive polyimide because of the following reasons.
First, the positive photosensitive polyimide has more excellent resolution than the negative photosensitive polyimide. Second, since the positive photosensitive polyimide has relatively smaller light irradiation area than the negative photosensitive polyimide, there is a low possibility of defects. Third, in the negative manner, since organic solvents such as N-methyl-2-pyrrolidone (NMP) or dimethyl acetamide (DMAc) are used as the developing solution, there are problems in views of environments such as cost, waste water treatment and the like. However, in the positive manner in which the alkali aqueous solution is used as the developing solution, cost is reduced and it is environmentally friendly.
To be specific, there are the following patent publications in respects to the positive photosensitive polyimide.
Japanese Unexamined Patent Application Publication Nos. 52-13315 and 62-135824 disclose a method for manufacturing a pattern using a difference between solubilities of an exposed portion and a non-exposed portion by mixing a polyamic acid as a polyimide precursor and a naphtoquinonediazide compound that is a dissolution inhibiting agent with each other. However, the method is problematic in that the difference between solubilities of the exposed portion and the non-exposed portion is not large enough to form a pattern having high resolution.
In addition, Japanese Unexamined Patent Application Publication No. 64-60630 discloses a method for mixing soluble polyimide that has a hydroxy group and a naphtoquinonediazide compound with each other. However, the method is problematic in that the addition content of photosensitizer is large, the structure of the polyimide precursor is limited, and physical properties are poor.
In addition, Japanese Unexamined Patent Application Publication No. 60-37550 discloses a method for performing ester bonding of an o-nitrobenzylester group that is a photosensitive group to a precursor. However, the method is problematic in that it is difficult to improve the thickness of the layer because of the low strength.
In addition, Japanese Unexamined Patent Application Publication Nos. 7-33874 and 7-134414 disclose a chemical amplification composition that is manufactured by mixing a resin that is obtained by substituting a carboxy group of a polyamic acid with an acetal group that is dissociated by an acid with a photoacid generating agent. However, there is a problem in that the residual layer ratio of the composition is excellent but the layer shrinkage is high after the curing and physical properties are poor.
As described above, although the positive photosensitive polyimide has many advantages, commercialization thereof has not been yet made up to the present because of the above problems which should be overcome.